Methods for enhancing permeation of a drug based on supply of a weak electrical current to the skin known as ion introduction or iontophoresis have been disclosed in the conventional art. Several specific examples of these methods will be hereinafter considered.
Ion introduction is based on formation of a closed circuit by, of a positive and negative electrode connected to a power supply, bringing the cathode thereof coated with, for example, a negatively ionized drug into contact at several locations with skin serving as a drug layer through which it is desirable that the drug be permeated and, using a separate location of skin having communication with the skin tissue mentioned above as a receiving layer, bringing the anode into contact with this layer whereupon, utilizing the electrical energy exerted on the drug of the drug layer when a current is conducted from the cathode to the drug layer as a result of a closed circuit being formed, the drug is permeated through the epidermis into the dermis and permeation is enhanced.
The ion introduction described above normally requires that the electrode polarity be kept constant and, accordingly, it uses a direct current power source. In addition, because a drop in drug permeation rate attributable to polarization of the skin caused by the passage of an electrical current is known to occur, there is a need for a voltage to be intermittently applied during the passage of an electrical current in order to prevent this from occurring which necessitates the assembly of a predetermined processor within a circuit designed to do this whereupon, accordingly, there is an inherent problem in this case from the viewpoint of the complexity of the device. In addition, there is an inherent drawback associated with the adoption of configuration that employs a battery as a direct power source from the viewpoint of the need for battery replacement. A typical example of an ion introducer of the type described here is disclosed in Japanese Patent Application No. H7-75882. In addition, while the use of an alternating current power source affords a simple device because it necessitates the assembly of a rectifying element such as a diode alone, there is an inherent drawback associated therewith from the viewpoint of the need for circuit connection with the power source.
On the other hand, as disclosed in Japanese Patent Application Laid-open No. 2004-87662, a so-called piezoelectric bimorph element comprising piezoelectric elements affixed top-to-bottom that generate a piezoelectric current as a result of application of stress, and that is able to produce an electromotive force when stress deformation occurs as a result by stress being imparted to these elements is known.
However, an ion introducer configured to use the electromotive force produced by stress deformation of a piezoelectric bimorph element as a power source has yet to be devised.    Cited reference 1: Japanese Unexamined Patent Application No. H7-75882    Cited reference 2: Japanese Unexamined Patent Application No. 2004-87662